1. Field of the Invention
The present invention relates to an anti-vibration apparatus.
2. Description of the Related Art
Along with the progress of precision enhancement of precision apparatuses such as electron microscopes and semiconductor exposure apparatuses, requirements for anti-vibration performance incorporated in these precision apparatuses become stricter. Hence, in order to improve the anti-vibration performance, an anti-vibration apparatus which compensates for vibrations of an installation base on which the anti-vibration apparatus is installed and feedforward-controls a force to be applied to an anti-vibration base has been proposed in Japanese Patent Laid-Open Nos. 2003-130128, 9-190957, 10-116120, and 10-169701.
FIG. 4 shows the arrangement of a conventional anti-vibration apparatus 1000. The anti-vibration apparatus 1000 includes an anti-vibration base 1001, a plurality of supporting mechanisms 1002 which support the anti-vibration base 1001, and a plurality of actuators 1003 which apply forces (control forces) to the anti-vibration base 1001. The number of actuators 1003 to be laid out is determined so as to be able to drive the anti-vibration base 1001 in six-axis directions (three axes of horizontal, vertical, and translational directions, and three axes of rotational directions about the respective axes) in terms of a layout space and cost. The anti-vibration apparatus 1000 includes a detection unit 1005 which detects vibrations of an installation base 1004, and a control unit 1009 including a calculation unit 1006 and distribution unit 1007. The calculation unit 1006 estimates vibrations transmitted to the anti-vibration base 1001 via the supporting mechanisms 1002 based on a detection result of the detection unit 1005, and calculates a force required to cancel these vibrations (a force to be applied to the anti-vibration base 1001). The distribution unit 1007 distributes the force calculated by the calculation unit 1006 into forces respectively applied by the actuators 1003 to the anti-vibration base 1001. In this way, the anti-vibration apparatus 100 improves the anti-vibration performance by feedforward-controlling the respective actuators 1003 so as to cancel vibrations transmitted from the installation base 1004 to the anti-vibration base 1001.
Japanese Patent Laid-Open No. 2003-130128 discloses a technique which allows to separately detect vibrations (behaviors) of the installation base as rigid body motion components and elastic deformation components in association with the arrangement and layout of the detection unit which detects vibrations of the installation base. Then, a force to be applied to the supporting mechanisms, which support the anti-vibration base, is calculated from the detection result of the detection unit, thereby calculating the force required for anti-vibration.
Japanese Patent Laid-Open No. 9-190957 discloses a technique associated with a distribution matrix (distribution ratio) required to distribute a force required to cancel vibrations transmitted to the anti-vibration base to the respective actuators. In Japanese Patent Laid-Open No. 9-190957, the distribution matrix is determined based on the relationship among the barycentric position of the anti-vibration base, the layout of the actuators, and directions of forces applied by the actuators to the anti-vibration base.
However, it becomes difficult for the conventional anti-vibration apparatus to attain high anti-vibration performance required for recent precision apparatuses. For example, the technique of Japanese Patent Laid-Open No. 9-190957 uses the distribution matrix determined based on the relationship among the barycentric position of the anti-vibration base, the layout of the actuators, and the directions of forces applied by the actuators to the anti-vibration base, that is, inertia information, and does not consider any rigidity information of the supporting mechanisms which support the anti-vibration base. Even when the force required to cancel vibrations transmitted to the anti-vibration base is distributed to the respective actuators using only such distribution matrix, sufficient anti-vibration performance cannot be obtained.
Japanese Patent Laid-Open No. 10-116120 discloses a technique for determining the distribution matrix in consideration of rigidity information of the supporting mechanisms which support the anti-vibration base. However, Japanese Patent Laid-Open No. 10-116120 does not disclose how to consider the rigidity information of the supporting mechanisms, that is, a distribution matrix which considers the rigidity information of the supporting mechanisms.
Japanese Patent Laid-Open No. 10-169701 discloses a technique for detecting forces acting on the respective supporting mechanisms which support the anti-vibration base in three directions (horizontal, vertical, and translational directions), and laying out a large number of actuators so as to apply forces to the anti-vibration base in directions opposite to these forces. However, since the anti-vibration apparatus is required to reduce the number of actuators as much as possible in terms of a layout space and cost, it is difficult to apply this technique to an actual anti-vibration apparatus.